1. Field of the invention
This invention relates generally to semiconductor device manufacturing, and, more particularly, to a method and apparatus for determining measurement frequency based on hardware age and usage.
2. Description of the Related Art
The manufacture of most devices, such as semiconductor devices, requires a number of discrete processing steps to create the device. For the example of semiconductor devices, a number of discrete steps are needed to produce a packaged semiconductor circuit device from raw semiconductor material. The starting substrate is usually a slice of single crystal silicon referred to as a wafer. Circuits of a particular type are fabricated together in batches of wafers called xe2x80x9clotsxe2x80x9d or xe2x80x9crunsxe2x80x9d. The fabrication process creates regular arrays of a circuit on the wafers of a lot. During processing, the individual wafers in a lot may go through individual processing steps one at a time or as a batch. At the completion of wafer processing, the wafers are tested to determine circuit functionality. Later the wafers are sliced, the functioning devices are packaged, and further testing occurs prior to use by the customer.
Data gathered during the course of wafer processing is used to diagnose yield problems and forms the basis of yield improvement efforts. Such performance measurements include defect count measurements, thickness measurements (i.e., indicative of deposition rate), and resistivity measurements, for example.
The number of defects is often predictable as a function of tool hardware life. The resistivity and deposition rate also change with hardware life, and/or maintenance history. For much deposition equipment, defects are more probable when the tool is first put together and at the end of its life. In a sputtering deposition tool, the source of metal to be sputtered is referred to as a target. The target is depleted as sputtering is conducted, and, thus, the target is changed frequently. The resistivity and/or deposition rate of the layer being deposited change slowly after a target change and after a wet clean.
In a chemical vapor deposition (CVD) tool, reactive gases are introduced into the processing chamber through a gas supply header, commonly referred to as a showerhead. Over time, process materials and/or byproducts collect on the showerhead, eventually leading to degraded performance. As the showerhead becomes obstructed, the deposition rate of the CVD tool decreases and becomes more erratic. The gas supplied to the showerhead often passes through an in-line filter. Over time, the filter may become obstructed, thus reducing the amount of reactive gases it passes. This reduction could also eventually cause a reduction in the deposition rate of the tool.
Current semiconductor processing techniques typically take performance measurements at a fixed rate (e.g., every fourth lot processed in a tool) or by pre-assigning a fixed percentage of lots for measurement. Because lots are not typically processed in a particular order, the percentage technique sometimes results in periods where multiple lots are measured consecutively, followed by periods where no lots are measured.
To address the stability problem identified above, preventative maintenance tasks, such as cleanings, tool refurbishment, showerhead replacement, in-line filter replacement, and target replacement, are scheduled at intervals that are less than the expected time where the likelihood of instabilities increases. These intervals, by nature, are conservative, and may result in the performance of the preventative maintenance task before it is actually necessary. Also, due to the limitations of the performance measurement intervals described above, degradation of the tool prior to the end of the preventative maintenance interval may not be readily identified. As a result defective wafers could be manufactured, necessitating costly re-work or scrapping of the wafers.
The present invention is directed to resolving one or all of the problems mentioned above.
One aspect of the present invention is seen in a processing line including a processing tool, a measurement tool, and an automatic process controller. The processing tool is adapted to process articles. The measurement tool is adapted to measure a characteristic of selected articles at a measurement frequency. The automatic process controller is adapted to change the measurement frequency based on a usage characteristic of the processing tool.
Another aspect of the present invention is seen in a method for monitoring a processing tool. The method includes processing a plurality of articles in the processing tool; measuring a characteristic of selected articles at a measurement frequency; and changing the measurement frequency based on a usage characteristic of the processing tool.